Method and apparatus for cracking oil with removal of tar



L. LINK Nov. 24, 1931.

METHOD AND APPARATUS FOR CRACKING OIL WITH REMOVAL OF TAR I Filed Oct. 16, 1928 Q m a A R NW @N ww A NN ow Q Q llllll'lV/A Eluoemtoz $31 Mat mug Patented Nov. 24, 1931 tion in the chamber.

- UNITED STATES" PATENT OFFICE,

Louis LINK, or BATON ROUGE,

LOUISIANA, ASSIGNOR TO STANDARD OIL DEVELOP- MENT OOMPAN Y, A. CORPORATION OF DELAWARE METHOD AND APPARATUS FOR CRACKING OIL WITH REMOVAL OF TAR Application filed bctober 1c, 1928. Serial No. 312,788.

This invention relates to improvements in cracking hydrocarbon oil in an apparatus comprising an elongated heating passageway discharging into an enlarged digesting or soaking chamber. The invention deals particularly with the control of coke forma- This control is effected by withdrawal of liquid oil having a tendline 23 leads from'the bottom of each tower to a return line 23 connected with the still.

Two branches 24 and lead from the drawofi lines 23 ofthe first four towers, and the branches of each pair discharge respectively into an accumulator 26 and condensers 27. The condensers are connected to receivers 28.

v Vapors from the last tower 21 flow through ency to produce coke, under conditions re -..-Iine 29 to the condenser and receiver 31.

lated to secure both a good and a mercha ntable fuel oil.

The invention will be fully understood from the following description read in connection with the accompanying drawings in which:

Fig. 1 is a diagrammatic side elevation of a cracking plant operated according to my yield of gasoline method; and

Fig. 2 is an enlarged vertical section of plate used in the tar withdrawal line.

Referring to the drawings, 1 denotes a cracking coil mounted in a furnace setting 2 and discharging through line 3 into a thermally insulated soaking drum 4. Any suit able equipment of this general character may i be used. The cracked product is taken o from the upper and lower portion of the drum by lines 5 and 6 respectively. The

line 6 is extendeddownwardly in the drum to a point near the bottom man-head. A

pressure control valve 7 is installedin line 5 and a block valve 8 in line'6. These two lines are connected, preferably by a Y-fitting 9 or an equivalent joint which will lead the two streams from the drum smoothly into a common release line 10. If the two streams collide at a sharp angle, coke may be de- The-release pipe 10 extends into a still 11 and has perforations 12 on its under side opening near the bottom of the still. Feed .oil is supplied to the still throughline 13 and residual liquid ma be withdrawn from it through outlet 14. apors pass through the still dome 15 and line 16 into the'first tower of a five tower series designated, 17,

18 19, 20 and 21. The upper part of each tower is connected with the lower part of the next in series by a pipe 22. A draw-ofi' Liquid is withdrawn from the last tower through a branch 32 leading to a condenser 33 and receiver 34 orto the accumulator line of tower 20. Valves 35, 36 and 37 are provided as shown for regulating the distribution of liquids'from the towers to the still, the accumulator, and the condensers.

Stock from the accumulator 26 is for- 'warded by. pump 38 through line 39 to the inlet end of cracking coil 1. It will be noted that in this system only distillate stocks are cracked in the manner described in my pending United States application, Serial No. 641,825, filed May 28, 1923. This particular system is described here merely for illustration and the present invention is not limited to it.

Feedstock may be passed also into the accumulator 26 through line 40. Duplicate coals, drums and accumulators may be provi ed.

I have found that coke formation in the,

proposals the present invention is not based. upon valve control of the tar outlet. On the:

contrary the size of the orifice is predetermined to release substantially exactly and uniformly the required amount of tar from the drum throughout the run.

Theprincipal limiting factors with reference to the size of the orifice are:

1. Too much tar must not be withdrawn; coke formation will be preventedby so doing, but the conversion to gasoline through the cracking e uipment will be greatly lowered and the uel cost correspondingly increased;

2. Tar containing sediment tending 'to form coke must be promptly released or the withdrawal line will be clogged.

There are four principal conditions to be considered in determining the release:

1. Character of charging stock; 2. Outlet temperature of the cracking coil;

3. Feed rate to the coil;

4. Pressure in the soaking drum.

Although it is sometimes possible to calculate the size of the orifice, using the foregoing data, I have found it simpler and more accurate to determine this bydirect experiment. If a test run shows no coke formation in the drum, the orifice is reduced; if too much coke is formed, the orifice is increased.

The best results are usually obtained when the drum contains afew inches of coke as alayer .on the walls atthe end of the run.

Examples of suitable orifice sizes are as follows: a

When running refinery gas oil in the equipment described, feed rate to the coil 5,000 gallons per hour, coil outlet temperature 850, F., and pressure in the 6 x 40' drum 260 pounds per square inch, the circular orifice in the tar release line should have a diameter of approximately When running Smackover crude or the like (overhead stock only passing through the coil), feed rate to the coil 4,000 gallons per hour, coil outlet temperature 865 F. and

pressure in the 6 x 40" drum 260 pounds per square inch, the orifice in the tar release line should have a diameter of approximately The orifice will usually be not less than A" or more than in diameter.

The feed rate to the coils should'be maintained as constant as possible throughout the run. Flow meters should be installed in the charging lines as regulation of flow by counting pump strokes cannot be relied upon ow-' ing'to slippage in the pumps. The pressure in the drum should also be kept substantially constant. This can be regulated by the valve 7.

The cracking coil and drum are-brought up to operating temperature in the usual manner. Valve 8 remains closed until the drum. is under full operating pressure. The valve is then opened and remains open all through the run. In a preferredoperation the orifice plate only determines the outflow of tar though the valve 8 may of course be operated if required for any reason. The tar tending to accumulate in the bottom of the drum is drawn off at the proper rate before hard or ,fixed coke can be formed and is immediately flux ed with the hot oil in still 11. The residu-' al oil produced meets commercial fuel oil specifications including the sediment test. The drum may be operated liquid phase or vapor-liquid phase. x I

The foregoingdescription is merely illustrative and various changes may be made within the scope of the appended claims, in which it is my intention to claim all novelty inherent in the invention as broadly as the prior art permits.

I claim:

1. In the operation of a. digesting drum for cracking hydrocarbon .oil, the improvement which comprises charging the drum with oil at high pressure and temperature, withdrawing the lighter cracked product from the upper part of said drum, withdrawing tar tending to form coke from the lower part of said drum through an opening of unvarying size predetermined in accordance with the .area not greater than a circle of about to diameter.

4. Method of cracking hydrocarbon oil of the type of gas oil, comprising passing the oil through a coil in which it attains a temperature of about 850 F. at the exit, discharging the oil into a thermally insulated digestion zone in which the oil is maintained at a pressure of about 260 lbs. per square inch, taking'ofi lighter cracked products from the upper part of the digestion zone, taking off "tar from a lower part of said; digestion zone throu h a circular orifice having an unvarying diameter of about discharging said lighter cracked products and tar into a zone of lower pressure, and supplying feed oil to thecracking coil at a rate of about 5,000 gal- .lons per hour.

5. In a digestion drum for cracking hydrocarbon oil, the improvement which comprises abottom draw-01f line from said drum, an

orifice plate having the opening therein de-' fined by a sharply beveled edge directed with its smaller cross-section toward the drum, and means for securing said plate in the drawoflf line.

' LOUIS LINK. 

